1. Field of the Invention
The invention relates generally to electrical switching apparatus and, more particularly, to conductor assemblies for electrical switching apparatus, such as circuit breakers. The invention also relates to flexible conductive elements for circuit breaker conductor assemblies.
2. Background Information
Electrical switching apparatus, such as circuit breakers, provide protection for electrical systems from electrical fault conditions such as, for example, current overloads, short circuits, abnormal voltage and other fault conditions. Typically, circuit breakers include an operating mechanism which opens electrical contact assemblies to interrupt the flow of current through the conductors of an electrical system in response to such fault conditions.
Many low-voltage circuit breakers, for example, employ a molded housing having two parts, a first half or front part (e.g., a molded cover), and a second half or rear part (e.g., a molded base). The operating mechanism for such circuit breakers is often mounted to the front part of the housing, and typically includes an operating handle and/or button(s) which, at one end, is (are) accessible from the exterior of the molded housing and, at the other end, is (are) coupled to a pivotable pole shaft. Electrical contact assemblies, which are also disposed within the molded housing, generally comprise a conductor assembly including a movable contact assembly having a plurality of movable contacts, and a stationary contact assembly having a plurality of corresponding stationary contacts. The movable contact assembly is electrically connected to a generally rigid conductor of the conductor assembly by flexible conductors, commonly referred to as shunts. The movable contact assembly includes a plurality of movable contact arms or fingers, each carrying one of the movable contacts and being pivotably coupled to a contact arm carrier. The contact arm carrier is pivoted by a protrusion or arm on the pole shaft of the circuit breaker operating mechanism to move the movable contacts into and out of electrical contact with the corresponding stationary contacts of the stationary contact assembly. The contact arm carrier includes a contact spring assembly structured to bias the fingers of the movable contact assembly against the stationary contacts of the stationary contact assembly in order to provide and maintain contact pressure when the circuit breaker is closed, and to accommodate wear.
The shunts typically comprise either copper wire ropes or layered copper ribbons, and are solidified at their ends using heat and pressure and then brazed to the rigid conductor at one end, and to the fingers of the movable contact assembly at the opposite end. One of the disadvantages associated with known wire rope or braided-type shunts is that they do not fit well within the limited spacing which is available between the adjacent fingers of the movable contact assembly. Specifically, the body of such shunts tends to expand outward and occupy more than the width of the finger, thus interfering with adjacent structures. The wire ropes also tend to bunch together during short circuit events, thus inhibiting the flexibility of the assembly. This is problematic in view of the compound motion which the fingers experience as a result of the well known “heel-toe” and/or “blow-on” arcing schemes which are commonly employed by low-voltage circuit breakers. See, e.g., U.S. Pat. No. 6,005,206, which is hereby incorporated herein by reference. Layered ribbon-type shunts also suffer from a number of unique disadvantages. Among them is the fact that they are typically V-shaped, thus having a single relatively sharp bend which undesirably creates an area of stress concentration. This V shape also consumes a substantial amount of valuable space within the molded housing of the circuit breaker.
There is a need, therefore, for elements (e.g., shunts) which have a high degree of flexibility, yet which are compact in their design and configuration and are rugged in order to accommodate and withstand the full range of movement (e.g., compound motion) of the movable contact assembly of the circuit breaker, while occupying minimal space within the molded housing of the circuit breaker.
There is, therefore, room for improvement of conductor assemblies for electrical switching apparatus such as, for example, low-voltage circuit breakers.